Method and apparatus for depositing tungsten after surface treatment to improve film characteristics

ABSTRACT

A method and system to form a refractory metal layer over a substrate includes introduction of a reductant, such as PH 3  or B 2 H 6 , followed by introduction of a tungsten containing compound, such as WF 6 , to form a tungsten layer. It is believed that the reductant reduces the fluorine content of the tungsten layer while improving the step coverage and resistivity of the tungsten layer. It is believed that the improved characteristics of the tungsten film are attributable to the chemical affinity between the reductants and the tungsten containing compound. The chemical affinity provides better surface mobility of the adsorbed chemical species and better reduction of WF 6  at the nucleation stage of the tungsten layer. The method can further include sequentially introducing a reductant, such as PH 3  or B 2 H 6 , and a tungsten containing compound to deposit a tungsten layer. The formed tungsten layer can be used as a nucleation layer followed by bulk deposition of a tungsten layer utilizing standard CVD techniques. Alternatively, the formed tungsten layer can be used to fill an aperture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent Application Ser. No. 60/305,765, filed Jul. 16, 2001, which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to the processing of semiconductor substrates. More particularly, embodiments of the invention relate to improvements in the process of depositing refractory metal layers on semiconductor substrates.

2. Description of the Related Art

The semiconductor processing industry continues to strive for larger production yields while increasing the uniformity of layers deposited on substrates having larger surface areas. These same factors in combination with new materials also provide higher density of circuits per unit area of the substrate. As circuit density increases, the need for greater uniformity and process control regarding layer thickness rises. As a result, various technologies have been developed to deposit layers on substrates in a cost-effective manner, while maintaining control over the characteristics of the layer. Chemical Vapor Deposition (CVD) is one of the most common deposition processes employed for depositing layers on a substrate. CVD is a flux-dependent deposition technique that requires precise control of the substrate temperature and precursors introduced into the processing chamber in order to produce a desired layer of uniform thickness. These requirements become more critical as substrate size increases (e.g., from 200 mm diameter substrates to 300 mm substrates), creating a need for more complexity in chamber design and gas flow technique to maintain adequate uniformity.

A variant of CVD that demonstrates superior step coverage compared to CVD, is Atomic Layer Deposition (ALD). ALD is based upon Atomic Layer Epitaxy (ALE) that was employed originally to fabricate electroluminescent displays. ALD employs chemisorption to deposit a saturated monolayer of reactive precursor molecules on a substrate surface. This is achieved by alternatingly pulsing an appropriate reactive precursor into a deposition chamber. Each injection of a reactive precursor is separated by an inert gas purge to provide an adsorbed atomic layer to previously deposited layers to form a uniform layer on the substrate. The cycle is repeated to form the layer to a desired thickness. A drawback with ALD techniques is that the deposition rate is much lower than typical CVD techniques by at least one order of magnitude.

Formation of film layers at a high deposition rate while providing adequate step coverage are conflicting characteristics often necessitating sacrificing one to obtain the other. This conflict is true particularly when refractory metal layers are deposited to cover apertures or vias during formation of contacts that interconnect adjacent metallic layers separated by dielectric layers. Historically, CVD techniques have been employed to deposit conductive material such as refractory metals in order to inexpensively and quickly fill vias. Due to the increasing density of semiconductor circuitry, tungsten has been used based upon superior step coverage to fill these high aspect ratio structures. As a result, deposition of tungsten employing CVD techniques enjoys wide application in semiconductor processing due to the high throughput of the process and good step coverage.

Depositing tungsten by traditional CVD methods, however, is attendant with several disadvantages. For example, blanket deposition of a tungsten layer on a semiconductor wafer is time-consuming at temperatures below 400° C. The deposition rate of tungsten may be improved by increasing the deposition temperature between approximately 500° C. to 550° C.; however, temperatures in this higher range may compromise the structural and operational integrity of the underlying portions of the integrated circuit being formed. Use of tungsten has also complicated photolithography steps during the manufacturing process as it results in a relatively rough surface having a reflectivity of 20% or less than that of a silicon substrate. Finally, tungsten has, proven difficult to deposit uniformly. Variance in film thickness of greater than 1% has been shown, thereby causing poor control of the resistivity of the layer. Several prior attempts to overcome the aforementioned drawbacks have been attempted.

For example, in U.S. Pat. No. 5,028,565 to Chang et al., which is assigned to the assignee of the present invention, a method is disclosed to improve, inter alia, uniformity of tungsten layers by varying the deposition chemistry. The method includes, in pertinent part, formation of a nucleation layer over an intermediate barrier layer before depositing the tungsten layer via bulk deposition. The nucleation layer is formed from a gaseous mixture of tungsten hexafluoride, hydrogen, silane and argon. The nucleation layer is described as providing a layer of growth sites to promote uniform deposition of a tungsten layer thereon. The benefits provided by the nucleation layer are described as being dependent upon the barrier layer present. For example, were the barrier layer formed from titanium nitride, the tungsten layer's thickness uniformity is improved as much as 15%. Were the barrier layer formed from sputtered tungsten or sputtered titanium tungsten, the benefits provided by the nucleation layer are not as pronounced.

A need exists, therefore, to provide techniques to improve the characteristics of refractory metal layers deposited on semiconductor substrates.

SUMMARY OF THE INVENTION

A method and system to form a refractory metal layer over a substrate includes introduction of a reductant, such as PH₃ or B₂H₆, followed by introduction of a tungsten containing compound, such as WF₆, to form a tungsten layer. It is believed that the reductant reduces the fluorine content of the tungsten layer while improving the step coverage and resistivity of the tungsten layer. It is believed that the improved characteristics of the tungsten film are attributable to the chemical affinity between the reductants and the tungsten containing compound. The chemical affinity provides better surface mobility of the adsorbed chemical species and better reduction of WF₆ at the nucleation stage of the tungsten layer.

The method can further include sequentially introducing a reductant, such as PH₃ or B₂H₆, and a tungsten containing compound to deposit a tungsten layer. The formed tungsten layer can be used as a nucleation layer followed by bulk deposition of a tungsten layer utilizing standard CVD techniques. Alternatively, the formed tungsten layer can be used to fill an aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a semiconductor processing system in accordance with the present invention

FIG. 2 is a schematic cross-sectional view of one embodiment of the processing chambers shown above in FIG. 1.

FIG. 3 is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a reductant over a substrate during sequential deposition.

FIG. 4 is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a refractory metal containing compound over the substrate after introduction of the reductant.

FIG. 5 is a graphical representation showing the concentration of gases present in a processing chamber, such as processing chamber as shown above in FIG. 2.

FIG. 6 is a graphical representation showing the relationship between the number of ALD cycles and the thickness of a layer formed on a substrate employing sequential deposition techniques, in accordance with the present invention.

FIG. 7 is a graphical representation showing the relationship between the number of sequential deposition cycles and the resistivity of a layer formed on a substrate employing sequential deposition techniques, in accordance with the present invention.

FIG. 8 is a graphical representation showing the relationship between the deposition rate of a layer formed on a substrate employing sequential deposition techniques and the temperature of the substrate.

FIG. 9 is a graphical representation showing the relationship between the resistivity of a layer formed on a substrate employing sequential deposition techniques and the temperature of the substrate, in accordance with the present invention.

FIG. 10 is a schematic cross-sectional view of one embodiment of a patterned substrate having a nucleation layer formed thereon employing sequential deposition techniques, in accordance with the present invention.

FIG. 11 is a schematic cross-sectional view of one embodiment of the substrate, shown above in FIG. 10, with a refractory metal layer formed atop of the nucleation layer employing CVD, in accordance with the present invention.

FIG. 12 is a graphical representation showing the concentration of gases present in a processing chamber, such as the processing chamber as shown above in FIG. 2, in accordance with an alternative embodiment of the present invention.

FIG. 13 is a graphical representation showing the concentration of gases present in a processing chamber, such as processing chamber as shown above in FIG. 2, in accordance with an alternative embodiment of the present invention.

FIG. 14 is a graphical representation showing the fluorine content versus depth of a refractory metal layer formed on a substrate employing ALD, either Ar or N₂ being a carrier gas.

FIG. 15 is a graphical representation showing the fluorine content versus depth of a refractory metal layer formed on a substrate employing ALD with H₂ being a carrier gas.

FIG. 16 is a schematic cross-sectional view of one embodiment of a substrate shown above in FIGS. 3 and 4 upon which a layer of either PH₃ or B₂H₆ is disposed between a substrate and a tungsten layer, in accordance with one embodiment of the present invention.

FIG. 17 is a graphical representation showing the concentration of gases present in a processing chamber, such as processing chamber as shown above in FIG. 2, in accordance with one embodiment of the present invention.

FIG. 18 is a schematic cross-sectional view of one embodiment of a substrate shown above in FIGS. 3 and 4 in which a titanium-containing layer is deposited between a substrate and a layer of either PH₃ or B₂H₆, in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an exemplary wafer processing system includes one or more processing chambers 12 and 14 disposed in a common work area 16 surrounded by a wall 18. Processing chambers 12 and 14 are in data communication with a controller 22 that is connected to one or more monitors, shown as 24 and 26. The monitors typically display common information concerning the process associated with processing chambers 12 and 14. One of the monitors 26 is mounted on wall 18, with the remaining monitor 24 being disposed in work area 16. Operational control of processing chambers 12 and 14 may be achieved by the use of a light pen, associated with one of the monitors 24 and 26, to communicate with controller 22. For example, light pen 28 is associated with monitor 24 and facilitates communication with controller 22 through monitor 24. Light pen 39 facilitates communication with controller 22 through monitor 26.

Referring both to FIGS. 1 and 2, each of processing chambers 12 and 14 includes a housing 30 having a base wall 32, a cover 34 disposed opposite to base wall 32, and a sidewall 36 extending therebetween. Housing 30 defines a chamber 37, and a pedestal 38 is disposed within processing chamber 37 to support a substrate 42, such as a semiconductor wafer. Pedestal 38 may be mounted to move between cover 34 and base wall 32, using a displacement mechanism (not shown), but the position thereof is typically fixed. Supplies of processing gases 39 a, 39 b and 39 c are in fluid communication with processing chamber 37 via a showerhead 40. Regulation of the flow of gases from supplies 39 a, 39 b and 39 c is effectuated via flow valves 41.

Depending on the specific process, substrate 42 may be heated to a desired temperature prior to layer deposition via a heater embedded within pedestal 38. For example, pedestal 38 may be resistively heated by applying an electric current from AC power supply 43 to heater element 44. Substrate 42 is, in turn, heated by pedestal 38, and can be maintained within a desired process temperature range of, for example, about 20° C. to about 750° C. A temperature sensor 46, such as a thermocouple, is also embedded in wafer support pedestal 38 to monitor the temperature of pedestal 38 in a conventional manner. For example, the measured temperature may be used in a feedback loop to control the electrical current applied to heater element 44 by power supply 43 such that the substrate temperature can be maintained or controlled at a desired temperature that is suitable for the particular process application. Optionally, pedestal 38 may be heated using radiant heat (not shown). A vacuum pump 48 is used to evacuate processing chamber 37 and to help maintain the proper gas flows and pressure inside processing chamber 37.

Referring to FIGS. 1 and 2, one or both of processing chambers 12 and 14, discussed above may operate to deposit refractory metal layers on the substrate employing sequential deposition techniques. One example of sequential deposition techniques in accordance with the present invention includes atomic layer deposition (ALD). The term “substrate” as used herein includes the substrate, such as semiconductor substrates and glass substrates, as well as layers formed thereover, such as dielectric layers (i.e., SiO₂) and barrier layers (i.e., titanium, titanium nitride and the like).

Not wishing to be bound by theory, FIG. 3 is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a reductant over a substrate during sequential deposition. The terms “adsorption” or “adsorb” as used herein are defined to include chemisorption, physisorption, or any attractive and/or bonding forces which may be at work and/or which may contribute to the bonding, reaction, adherence, or occupation of a portion of an exposed surface of a substrate structure. During the sequential deposition technique, in accordance with the present invention, a batch of a first processing gas, in this case “Aa_(x),” results in a layer of “A” being deposited on substrate 42 having a surface of ligand “a” exposed to processing chamber 37. Layer “A” may be a monolayer, more than a monolayer, or less than a monolayer. Thereafter, a purge gas enters processing chamber 37 to purge gas “Aa_(x),” which has not been incorporated into the layer of A. FIG. 4 is a schematic cross-sectional view of a substrate showing one possible mechanism of adsorption of a refractory metal containing compound over the substrate after introduction of the reductant. After purging gas “Aa_(x)” from processing chamber 37, a second batch of processing gas, “Bb_(y),” is introduced into processing chamber 37. The “a” ligand present on the substrate surface reacts with the “b” ligand and “B” atom, releasing molecules, for example, “ab” and “aA,” which move away from substrate 42 and are subsequently pumped from processing chamber 37. In this manner, a surface comprising a layer of B compound remains upon substrate 42 and exposed to processing chamber 37, shown in FIG. 4. The composition of the layer of B compound may be a monolayer or less of atoms typically formed employing ALD techniques. In other embodiments, more than a monolayer of B compound may be formed during each cycle. Alternatively, the layer of compound B may include a layer of multiple atoms (i.e. other atoms besides atoms of B). In such a case, the first batch and/or the second batch of processing gases may include a mixture of process gases, each of which has atoms that would adhere to substrate 42. The process proceeds cycle after cycle, until the desired thickness is achieved.

Referring to both FIGS. 3 and 4, although any type of processing gas may be employed, in the present example, the reductant “Aa_(x)” may comprise B₂H₆ or PH₃ and the refractory metal containing compound, Bb_(y), may comprise WF₆. Some possible reactions are shown below in reference to chemical reaction (1) and chemical reaction (2).

 B₂H₆(g)+WF₆(g)→W(s)+2BF₃(g)  (1) PH₃(g)+WF₆(g)→W(s)+PF₃(g)  (2) Other by-products include but are not limited to H₂, HF, F₂. Other reactions are also possible, such as decomposition reactions. In other embodiments, other reductants may be used, such as SiH₄. Similarly, in other embodiments, other tungsten containing gases may be used, such as W(CO)₆.

The purge gas includes Ar, He, N₂, H₂, other suitable gases, and combinations thereof. One or more purge gas may be used. FIG. 5 is a graphical representation of one embodiment of gases present in a processing chamber utilizing two purge gases Ar and N₂. Each of the processing gases was flowed into processing chamber 37 with a carrier gas, which in this example was one of the purge gases. WF₆ is introduced with Ar and B₂H₆ is introduced with N₂. It should be understood, however, that the purge gas may differ from the carrier gas, discussed more fully below. One cycle of the ALD technique in accordance with the present invention includes flowing the purge gas, N₂, into processing chamber 37 during time t₁, which is approximately about 0.01 to about 15 seconds before B₂H₆ is flowed into processing chamber 37. During time t₂, the processing gas B₂H₆ is flowed into processing chamber 37 for a time in the range of about 0.01 to about 15 seconds, along with a carrier gas, which in this example is N₂. After about 0.01 to about 15 seconds have lapsed, the flow of B₂H₆ terminates and the flow of N₂ continues during time t₃ for an additional time in the range of about 0.01 to about 15 seconds, purging the processing chamber of B₂H₆. During time t₄ which lasts approximately about 0 to about 30 seconds, processing chamber 37 is pumped so as to remove most, if not all, gases. After pumping of process chamber 37, the carrier gas Ar is introduced for a time in the range of about 0.01 to about 15 seconds during time t₅, after which time the process gas WF₆ is introduced into processing chamber 37, along with the carrier gas Ar during time t₆. The time t₆ lasts between about 0.01 to about 15 seconds. The flow of the processing gas WF₆ into processing chamber 37 is terminated approximately about 0.01 to about 15 seconds after it commenced. After the flow of WF₆ into processing chamber 37 terminates, the flow of Ar continues for an additional time in the range of 0.01 to 15 seconds, during time t₇. Thereafter, processing chamber 37 is pumped so as to remove most, if not all, gases therein, during time t₈. As before, time t₈ lasts approximately about 0 to about 30 seconds, thereby concluding one cycle of the sequential deposition technique, in accordance with the present invention. The cycle may be repeated to deposit a tungsten layer to a desired thickness.

The benefits of employing the sequential deposition technique are many fold, including flux-independence of layer formation that provides uniformity of deposition independent of the size of a substrate. For example, the measured difference of the layer uniformity and thickness measured between a 200 mm substrate and a 300 mm substrate deposited in the same chamber is negligible. This is due to the self-limiting characteristics of the sequential deposition techniques. Further, this technique contributes to improved step coverage over complex topography.

In addition, the thickness of the layer B, shown in FIG. 4, may be easily controlled while minimizing the resistance of the same by employing sequential deposition techniques. With reference to FIG. 6, it is seen in the slope of line 50 that the thickness of the tungsten layer B is proportional to the number of cycles employed to form the same. The resistivity of the tungsten layer, however, is relatively independent of the thickness of the layer, as shown by the slope of line 52 in FIG. 7. Thus, employing sequential deposition techniques, the thickness of a refractory metal layer maybe easily controlled as a function of the cycling of the process gases introduced into the processing chamber with a negligible effect on the resistivity.

FIG. 8 is a graphical representation showing the relationship between the deposition rate of a layer formed on a substrate employing sequential deposition techniques and the temperature of the substrate. Control of the deposition rate was found to be dependent upon the temperature of substrate 42. As shown by the slope of line 54, increasing the temperature of substrate 42 increased the deposition rate of the tungsten layer B. The graph shows that less than a monolayer, a monolayer, or more than a monolayer of a tungsten layer may be formed depending on the substrate temperature utilized. For example, at 56, the deposition rate is shown to be approximately 2 Å/cycle at 250° C. However at point 58 the deposition rate is approximately 5 Å/cycle at a temperate of 450° C. The resistivity of the tungsten layer, however, is virtually independent of the layer thickness, as shown by the slope of curve 59, shown in FIG. 9. As a result, the deposition rate of the tungsten layer may be controlled as a function of temperature without compromising the resistivity of the same. However, it may be desirable to reduce the time necessary to deposit an entire layer of a refractory metal.

To that end, a bulk deposition of the refractory metal layer may be included in the deposition process. Typically, the bulk deposition of the refractory metal occurs after the nucleation layer is formed in a common processing chamber. Specifically, in the present example, nucleation of a tungsten layer occurs in chamber 12 employing the sequential deposition techniques discussed above, with substrate 42 being heated in the range of about 200° C. to about 400° C., and processing chamber 37 being pressurized in the range of about 1 to about 10 Torr. A nucleation layer 60 of approximately about 120 to about 200 Å is formed on a patterned substrate 42, shown in FIG. 10. Nucleation layers of about 100 Å or less, about 50 Å or less, or about 25 Å or less have also been found to be effective in providing good step coverage over apertures having an aspect ratio of about 6:1 or greater. As shown, substrate 42 includes a barrier layer 61 and a patterned layer having a plurality of vias 63. The nucleation layer is formed adjacent to the patterned layer covering vias 63. As shown, forming nucleation layer 60 employing ALD techniques provides good step coverage. In another embodiment, sequential deposition techniques may be performed for both nucleation and bulk deposition. In still another embodiment, to decrease the time required to form a complete layer of tungsten, a bulk deposition of tungsten onto nucleation layer 60 occurs using CVD techniques, while substrate 42 is disposed in the same processing chamber 12, shown in FIG. 1. The bulk deposition may be performed using recipes well known in the art. In this manner, a tungsten layer 65 providing a complete plug fill is achieved on the patterned layer with vias having aspect ratios of approximately 6:1, shown in FIG. 11.

In an alternative embodiment, a bifurcated deposition process may be practiced in which nucleation of the refractory metal layer occurs in a chamber that is different from the chamber in which the remaining portion of the refractory metal layer is formed. Specifically, in the present example, nucleation of a tungsten layer occurs in chamber 12 employing the sequential deposition techniques, such as ALD, discussed above. To that end, substrate 42 is heated in the range of about 200° C. to about 400° C. and chamber 37 is pressurized in the range of about 1 to about 10 Torr. A nucleation layer 60 of approximately 120 to 200 Å is formed on a patterned substrate 42, shown in FIG. 10. Nucleation layers of about 100 Å or less, about 50 Å or less, or about 25 Å or less have also been found to be effective in providing good step coverage over apertures having an aspect ratio of about 6:1 or greater. As shown, substrate 42 includes a barrier layer 61 and a patterned layer having a plurality of vias 63. The nucleation layer is formed adjacent to the patterned layer covering the vias 63. As shown, forming the nucleation layer 60 employing sequential deposition techniques provides improved step coverage.

In one embodiment, sequential deposition techniques are employed for bulk deposition of tungsten onto nucleation layer 60 occurs while substrate 42 is disposed in processing chamber 14, shown in FIG. 1. The bulk deposition maybe performed using recipes disclosed herein. In another embodiment, CVD techniques are employed for bulk deposition of tungsten onto nucleation layer 60 occurs while substrate 42 is disposed in processing chamber 14, shown in FIG. 1. The bulk deposition maybe performed using recipes well known in the art. Whether sequential deposition or CVD deposition techniques are employed, a tungsten layer 65 providing a complete plug fill is achieved on the patterned layer with vias having aspect ratios of approximately 6:1, shown in FIG. 11. Implementing the bifurcated deposition process discussed above may decrease the time required to form a tungsten layer having improved characteristics. Utilizing CVD deposition techniques for bulk deposition may further increase throughput.

As mentioned above, in an alternate embodiment of the present invention, the carrier gas may differ from the purge gas, as shown in FIG. 12. The purge gas, which is introduced at time intervals t₁, t₃, t₅ and t₇ comprises Ar. The carrier gas, which is introduced at time intervals t₂ and t₆, comprises of N₂. Thus, at time interval t₂ the gases introduced into the processing chamber include a mixture of B₂H₆ and N₂, and a time interval t₆, the gas mixture includes WF₆ and N₂. The pump process during time intervals t₄ and t₈ is identical to the pump process discussed above with respect to FIG. 5. In yet another embodiment, shown in FIG. 13, the carrier gas during time intervals t₂ and t₆ comprises H₂, with the purge gas introduced at time intervals t₁, t₃, t₅ and t₇ comprising of Ar. The pump processes at time intervals t₄ and t₈ are as discussed above, As a result, at time interval t₂ the gas mixture introduced into processing chamber 37 comprises of B₂H₆ and H₂, and WF₆, and H₂ at time interval t₆.

An advantage realized by employing the H₂ carrier gas is that the stability of the tungsten layer B may be improved. Specifically, by comparing curve 66 in FIG. 14 with curve 68 in FIG. 15, it is seen that the concentration of fluorine in the nucleation layer 60, shown in FIG. 10, is much less when H₂ is employed as the carrier gas, as compared with use of N₂ or Ar as a carrier gas.

Referring to both FIGS. 14 and 15, the apex and nadir of curve 66 show that the fluorine concentration reaches levels in excess of 1×10²¹ atoms per cubic centimeter and only as low as just below 1×10¹⁹ atoms per cubic centimeter. Curve 68, however, shows that the fluorine concentration is well below 1×10²¹ atoms per cubic centimeter at the apex and well below 1×10¹⁷ atoms per cubic centimeter at the nadir. Thus, employing H₂ as the carrier gas provides a much more stable film, i.e., the probability of fluorine diffusing into the substrate, or adjacent layer is reduced. This also reduces the resistance of the refractory metal layer by avoiding the formation of a metal fluoride that may result from the increased fluorine concentration. Thus, the stability of the nucleation layer, as well as the resistivity of the same, may be controlled as a function of the carrier gas employed. This is also true when a refractory metal layer is deposited entirely employing ALD techniques, i.e., without using other deposition techniques, such as CVD.

In addition, adsorbing a layer 70, shown in FIG. 16, of either PH₃ or B₂H₆ prior to introduction of the tungsten containing compound forms a tungsten layer 72 with reduced fluorine content, improved step coverage, and improved resistivity. This was found to be the case where the tungsten containing compound is introduced over a layer of PH₃ or B₂H₆ employing sequential deposition techniques or employing standard CVD techniques using either tungsten hexafluoride, WF₆, and silane, SiH₄, or tungsten hexafluoride, WF₆, and molecular hydrogen, H₂, chemistries. The improved characteristics of the tungsten film are believed to be attributable to the chemical affinity between the PH₃ or B₂H₆ layer and the WF₆ layer. This provides better surface mobility of the adsorbed chemical species and better reduction of WF₆ at the nucleation stage of the tungsten layer. This has proven beneficial when depositing a tungsten layer adjacent to a titanium containing adhesion layer formed from titanium, Ti, or titanium nitride, TiN. Layer 70 is preferably a monolayer, but in other embodiments may be less than or more than a monolayer. Layer 70 in the film stack, shown in FIG. 16, shows the formation of the tungsten layer 72. It is understood that layer 70 may or may not be consumed during formation of the tungsten layer 72. It is also understood that a plurality of layers 70 and tungsten layers 72 may be deposited to form a tungsten layer to a desired thickness. As shown, layer 70 is deposited on substrate 74 that includes a wafer 76 that may be formed from any material suitable for semiconductor processing, such as silicon. One or more layers, shown as layer 74, may be present on wafer 76. Layer 78 may be formed from any suitable material, included dielectric or conductive materials. Layer 78 includes a void 80, exposing a region 82 of wafer 76.

FIG. 18 is a detailed cross-sectional view of a substrate in which a titanium-containing adhesion layer is formed between a substrate and a layer of either PH₃ or B₂H₆ during the fabrication of a W layer adjacent to the titanium-containing adhesion layer. The titanium-containing adhesion layer may be formed employing standard CVD techniques. In one embodiment, the titanium-containing adhesion layer is formed employing sequential deposition techniques. To that end, processing gas Aa_(x) is selected from the group including H₂, B₂H₆, SiH₄ and NH₃. Processing gas Bb_(y) is a titanium-containing gas selected from the group that includes TDMAT, TDEAT and TiCl₄. Also, Ar and N₂ purge gases are preferably employed, although other purge gas may be used.

Referring to FIGS. 2 and 17, each of the processing gases is flowed into processing chamber 37 with a carrier gas, which in this example, is one of the purge gases. It should be understood, however, that the purge gas may differ from the carrier gas, discussed more fully below. One cycle of the sequential deposition technique, in accordance with the present invention, includes flowing a purge gas into processing chamber 37 during time t₁ before the titanium-containing gas is flowed into processing chamber 37. During time t₂, the titanium-containing processing gas is flowed into the processing chamber 37, along with a carrier gas. After t₂ has lapsed, the flow of titanium-containing gas terminates and the flow of the carrier gas continues during time t₃, purging the processing chamber of the titanium-containing processing gas. During time t₄, the processing chamber 37 is pumped so as to remove all gases. After pumping of process chamber 37, a carrier gas is introduced during time t₅, after which time the reducing process gas is introduced into the processing chamber 37 along with the carrier gas, during time t₆. The flow of the reducing process gas into processing chamber 37 is subsequently terminated. After the flow of reducing process gas into processing chamber 37 terminates, the flow of carrier gas continues, during time t₇. Thereafter, processing chamber 37 is pumped so as to remove all gases therein, during time t₈, thereby concluding one cycle of the sequential deposition technique in accordance with the present invention. The aforementioned cycle is repeated multiple times until titanium-containing layer reaches a desired thickness. For example, in reference to FIG. 18, after TiN layer 84 reaches a desired thickness, layer 86, in this example formed from PH₃ or B₂H₆, is deposited adjacent thereto employing sequential deposition techniques, as discussed above. Thereafter, a layer of tungsten 88, shown in FIG. 18, is disposed adjacent to layer 86 using the sequential deposition technique or standard CVD techniques, both of which are discussed above. Layer 86 is preferably a monolayer, but in other embodiments may be less than or more than a monolayer. Layer 86 in the film stack, shown in FIG. 18, shows the formation of the tungsten layer 88. It is understood that layer 86 may or may not be consumed during formation of the tungsten layer 88. It is also understood that a plurality of layers 86 and tungsten layers 66 may be deposited to form a tungsten layer to a desired thickness. If desired, a copper layer maybe deposited atop of tungsten layer 88. In this manner, tungsten may function as a barrier layer.

Referring again to FIG. 2, the process for depositing the tungsten layer may be controlled using a computer program product that is executed by controller 22. To that end, controller 22 includes a central processing unit (CPU) 90, a volatile memory, such as a random access memory (RAM) 92 and permanent storage media, such as a floppy disk drive for use with a floppy diskette, or hard disk drive 94. The computer program code can be written in any conventional computer readable programming language; for example, 68000 assembly language, C, C++, Pascal, Fortran and the like. Suitable program code is entered into a single file, or multiple files, using a conventional text editor and stored or embodied in a computer-readable medium, such as hard disk drive 94. If the entered code text is in a high level language, the code is compiled and the resultant compiler code is then linked with an object code of precompiled Windows® library routines. To execute the linked and compiled object code, the system user invokes the object code, causing the CPU 90 to load the code in RAM 92. The CPU 90 then reads and executes the code to perform the tasks identified in the program.

Although the invention has been described in terms of specific embodiments, one skilled in the art will recognize that various changes to the reaction conditions, i.e., temperature, pressure, film thickness and the like can be substituted and are meant to be included herein. Additionally, while the bifurcated deposition process has been described as occurring in a common system, the bulk deposition may occur in a processing chamber of a mainframe deposition system that is different from the mainframe deposition system in which the processing chamber is located that is employed to deposit the nucleation layer. Finally, other refractory metals may be deposited, in addition to tungsten, and other deposition techniques may be employed in lieu of CVD. For example, physical vapor deposition (PVD) techniques, or a combination of both CVD and PVD techniques may be employed. The scope of the invention should not be based upon the foregoing description. Rather, the scope of the invention should be determined based upon the claims recited herein, including the full scope of equivalents thereof. 

1. A method of sequential deposition of a tungsten nucleation layer and a bulk tungsten layer over a substrate in a processing chamber, comprising: introducing a pulse of reducing gas comprising phosphine; introducing a tungsten containing compound to form the nucleation layer; and: forming the bulk tungsten layer over the tungsten nucleation layer.
 2. A method of depositing a tungsten layer over a substrate in a processing chamber, comprising: adsorbing a layer over the substrate comprising phosphine; and introducing a tungsten containing compound to form a tungsten layer, wherein introducing the tungsten containing compound comprises introducing the tungsten containing compound in a sequential deposition technique.
 3. A method of forming a tungsten layer over a substrate in a processing chamber, comprising: presoaking the substrate with phosphine to form a presoak layer over the substrate; and forming a tungsten layer over the presoak layer by sequentially introducing pulses of a tungsten-containing compound and pulses of a reductant.
 4. The method of claim 3, wherein the substrate is presoaked and the tungsten layer is formed in the same processing chamber.
 5. The method of claim 3, wherein the reductant is selected from the group consisting of hydrogen, silane, diborane and phosphine.
 6. The method of claim 3, further comprising introducing a purge gas at least partially between the pulses of the reductant and the pulses of the tungsten containing compound.
 7. The method of claim 3, wherein the substrate comprises a titanium-containing layer and the presoak layer is formed over the titanium-containing layer.
 8. The method of claim 3, wherein the tungsten layer is a tungsten nucleation layer.
 9. The method of claim 8, further comprising forming a bulk tungsten layer over the tungsten nucleation layer.
 10. A method of forming a tungsten layer on a substrate in a processing chamber, comprising: presoaking the substrate with phosphine to form a presoak layer on the substrate; and forming the tungsten layer on the presoak layer by an ALD process comprising: flowing a tungsten-containing compound into the processing chamber; chemisorbing the tungsten-containing compound to the presoak layer; purging the processing chamber with a purge gas; flowing a reductant selected from the group consisting of hydrogen, silane, diborane and phosphine into the processing chamber; and purging the processing chamber with the purge gas.
 11. The method of claim 10, wherein the substrate is presoaked and the tungsten layer is formed in the same processing chamber.
 12. The method of claim 10, wherein the reductant is diborane.
 13. The method of claim 10, wherein the purge gas is selected from the group consisting of Ar, He, H₂, N₂ and combinations thereof.
 14. The method of claim 10, wherein the substrate comprises a titanium-containing layer and the presoak layer is formed over the titanium-containing layer.
 15. The method of claim 10, wherein the tungsten layer is a tungsten nucleation layer.
 16. The method of claim 15, further comprising forming a bulk tungsten layer over the tungsten nucleation layer.
 17. The method of claim 8, wherein the bulk tungsten layer is deposited by a process selected from the group consisting of ALD, CVD, PVD or combinations thereof.
 18. The method of claim 16, wherein the bulk tungsten layer is deposited by a process selected from the group consisting of ALD, CVD, PVD or combinations thereof.
 19. A method of forming a tungsten layer on a substrate in a processing chamber, comprising: sequentially pulsing a tungsten containing compound and phosphine by an ALD process to deposit a nucleation tungsten layer; and forming a bulk tungsten layer over the nucleation tungsten layer.
 20. The method of claim 19, wherein the ALD process further comprises a purge gas selected from the group consisting of Ar, He, H₂, N₂ and combinations thereof.
 21. The method of claim 20, wherein the nucleation tungsten layer is deposited on a barrier layer selected from the group consisting of titanium, titanium nitride and combinations thereof.
 22. The method of claim 21, wherein the bulk tungsten layer is deposited by a process selected from the group consisting of ALD, CVD, PVD or combinations thereof. 